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Articles

Translucent Tissue Defects in Solanum tuberosum L

I. Alterations in Amyloplast Membrane Integrity, Enzyme Activities, Sugars, and Starch Content ¹

Department of Horticulture and Landscape Architecture, University of Minnesota, St. Paul, Minnesota 55108, Red River Valley Potato Research Laboratory ^,5, 311 5th Avenue NE, East Grand Forks, Minnesota 56721, United States Department of Agriculture, Metabolism and Radiation Research Laboratory, Fargo, North Dakota 58105

Kennebec (cv) potatoes randomly developed translucent areas in their centrally located pith-parenchymal cells during storage. These defective areas were characterized as having reduced starch concentration and increased levels of free sugars (i. e. sucrose and glucose) and inorganic phosphate. Electron micrographs of potato tubers stored at 10° ± 1°C for 8 months indicated that the amyloplast membrane was still intact and continuous around starch granules in both normal and prematurely sweetened tissue. The total activities of phosphorylase and sucrose-6-P synthase were elevated 5.4- and 3.8-fold, respectively, in the defective tissue compared to healthy nonsweetened tubers while there were no significant differences in the levels of sucrose synthase, UDPglucose pyrophosphorylase, invertase, or -amylase. Total and specific activities of acid phosphatase were only slightly elevated in translucent tissue but their increase was significant (P < 0.05, t test) over that seen in healthy tubers. The premature sweetening in storage may have been indirectly triggered by moisture and heat stress experienced during development. Translucency eventually led to physical deterioration of the tissue.

³ Research Chemist, United States Department of Agriculture, Agricultural Research Service Northern States Area.

⁴ Present Address: 376 Washington Avenue No. 1, Sunnyvale, CA 94086.

¹ Agricultural Experiment Station, University of Minnesota Scientific Journal Series 14,066.

⁵ A laboratory cooperatively operated by the Northern States Area, Agricultural Research Service, United States Department of Agriculture; The Minnesota Agricultural Experiment Station; The North Dakota Agricultural Experiment Station; and the Red River Valley Potato Grower's Association.